What the Study Looked At

The study involved eight anonymous moms of children aged three to five months, all of whom regularly smoked cannabis. After ingesting a controlled dosage, women provided researchers with breast milk samples, which were then tested for THC and its metabolites. Researchers tested the milk 20 minutes after subjects smoked, and then at one-, two-, and four-hour intervals.

What the Study Found

The tests showed that the breast milk had the highest THC levels one hour after the subjects had smoked cannabis, which was legally obtained from a dispensary in Colorado. The researchers stated that babies who were exclusively breastfed ingested an estimated 2.5 percent of the maternal dose of THC, or, over the course of the day about 8 micrograms of THC per kilogram per day. (Researchers pointed out that THC affects the central nervous system for about two hours and typically takes 20 to 36 hours to be eliminated from the body.)

“The levels are low in the milk, and even less would be absorbed by the infants,” study author Tom Hale, PhD, professor of pediatrics at the Texas Tech University School of Medicine, executive director of the school’s InfantRisk Center, told Healthline.

That said, Hale and his colleagues concluded, “It remains unclear what exposure to cannabis products during this critical neurobehavioral development period will mean for the infant.”

What This Means for Parents

While this study adds to a growing body of research that's helpful for parents-to-be to consider, the jury is still very much out on exactly how marijuana use during pregnancy or while you're breastfeeding affects your baby in utero or a breastfeeding baby. Not to mention that under Colorado state law, physicians who take blood tests that show any level of THC in a child blood test are obligated under state law to inform child protective services.

The bottom line: As Hale tells Healthline, “While it’s legal to use cannabis in Colorado, it’s not legal if you’re pregnant or breastfeeding.” And regardless of his study’s findings, he advises that women steer clear of marijuana while nursing or expecting. Given the various questions about cannabis’ effect on pediatric health that still need to be answered, that's good advice to follow.

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Maressa Brown is an editor and writer with more than a decade of experience covering lifestyle, pop culture, and parenting. Her work has appeared in/on a variety of publications including Cosmopolitan.com, Parents.com, Romper, Redbookmag.com, ELLE.com, GoodHousekeeping.com, Bustle, Variety, Women's Health, and Better Homes & Gardens. She loves researching and covering women’s health, beauty/style, relationships, pop culture, and astrology. Follow her on Twitter @MaressaSylvie.